The invention relates to a three-way or multi-way valve, which is built up of a plurality of two-way valves, each of which has a high pressure connection and a low pressure connection which are separated from each other by means of a valve seat with which a closure element co-operates, the two-way valves being arranged to be operated in pairs or in groups by means of a control pressure fluid by way of a control pressure line opening into a pressure chamber, and one of the two-way valves (pump valve) of each group being arranged in a connection between a pressure source and a load, and another two-way valve (tank valve) of the same groups being arranged in a connection between the load and a pressure sink.
A valve of this type is known from DE 22 58 853 B2. The two-way valves are in that case built up in the manner of a bridge, in which the individual two-way valves are arranged in the arms of the bridge, the load is connected up by way of one diagonal of the bridge, and the other diagonal lies between a pump acting as pressure source and a tank acting as pressure sink. The two-way valves are actuated by means of control valves which raise or lower the pressure in the pressure chamber.
Valves of this type are used as hydraulic valves for controlling fluid flow and fluid pressures. They function without any problem, as long as oil, especially a synthetic hydraulic oil, is used as hydraulic fluid.
For some time, however, attempts have been made to replace the hydraulic oils, especially the synthetic hydraulic oils, by means of water, because of their somewhat questionable properties, from the environmental point of view, and especially of their toxicity. However, water has practically no lubricating properties, and, moreover, in many cases leads to corrosion damage, so that valves of this type wear out relatively quickly, or even seize up, so that they can no longer fulfil their function or can no longer do so to a satisfactory degree.
A two-way seat-type valve has therefore already been proposed (DE 36 37 208 C2) for fluids consisting essentially of water, in which the closure element of the two-way valve is prevented from coming into contact with the guide, that is to say, with the housing surrounding it. For this purpose, sliding rings of plastics material are provided which surround the closure element. Between two sliding rings of this type a seal is arranged. At all events, the closure element of such a valve offers a resistance to movement which is somewhat considerable, and is caused by the sliding rings and the sealing rings. A pre-requisite for a valve of this type is therefore the necessary pressure build up for both directions of movement of the closure element. This is provided, for example, in DE 22 58 853 B2 by the possibility of connecting the control pressure line to the pump by way of a control valve. This, however, entails a relatively complex construction of the valve and makes operation more difficult.
The problem underlying the invention is that of obtaining good closing behaviour with simple operation.